By mid-June, there was almost no shadow of yellow croaker in the vast Qinghai Lake, but there was a spectacular scene of "half river with clear water and half river fish" in the river. Hundreds of millions of fish swam against the current and swam upstream all the way, the farthest distance was 60 or 70 kilometers. It seemed as if they were laying eggs while swimming, but in fact, it was very difficult and even faced with death, but they were fearless and still smart to go upstream ...
This is the migration of yellow croaker, the instinct to prolong life and the miracle to trace the origin of life.
The beautiful scenery painted by the elves of Qinghai Lake.
Starting from Xining in the morning, the target is the Shaliu River, all the way to the west. Looking at the grassland against the blue sky and white clouds, my heart is becoming more and more quiet. Driving hundreds of kilometers, just to witness a spectacular sight of yellow croaker migration.
At noon, as the temperature rises, more and more fish gather in the Shaliu River in gangcha county, which soon becomes a dense school of fish, slowly moving upstream against the current. Occasionally, a few seem to be tired of swimming for a short period downstream with the current, and then turn around and strive to go upstream, so repeatedly but without flinching. In the narrow water area of more than 20 square meters in front of a steep slope in the river, the number of yellow croaker has been countless, and the bottom of the water can't be seen. Only the backs of countless black fish can be seen, and a large number of yellow croaker have formed a gathering trend. At this time, the underwater yellow croaker has already presented a scene of "half river water and half river fish". Suddenly, a fish jumped up and "flew" into the river on the steep slope. Then more and more fish jumped up and twisted their bodies gracefully in the air, accompanied by splashing water. It was a rare beauty.
Going upstream is to find the stimulation of water flow.
Many fish in the world have migratory habits, including fish in the sea and fish in the river, such as Chinese sturgeon and salmon. So why do yellow croaker migrate? Shi Jianquan, director of Qinghai Lake Naked Carp Rescue Research Center, said: "Because of the development of gonads, it needs the stimulation of a current. Every year from May to August, it is reached. In other words, it should immediately start preparing for this stage of reproduction. At this stage, it needs the stimulation of water flow to make its gonads mature. " It turns out that the yellow croaker went upstream along the river to find excitement. Without the stimulation of running water, the eggs of female fish can't mature, and the sperm of male fish can't mature, so the task of carrying on the family line can't be completed. Therefore, when the male fish reaches the age of 3 and the female fish reaches the age of 4, they will go to the running water every summer, looking for excitement and waiting for the moment of energy explosion in their lives.
Performing water ballet for the continuation of life
The reproduction of yellow croaker is carried out by in vitro fertilization. The female fish discharges the eggs into the water, and the male fish also discharges the sperm into the water, so that the eggs and sperm can find their own objects in the water, so the spawning ground chosen by the fish mother and the fish father is very particular. Generally speaking, the yellow croaker will choose some places where the water flow is relatively gentle, the water depth is relatively suitable, and the bottom material is some small sand and gravel as the spawning ground. The water flow is slow, and there are small gravel under the water to dig holes, so you can make a nest for the children. Sperm and eggs are not easy to be washed away, and there are more opportunities for fertilization. The high temperature in shallow water will also be beneficial to the hatching of fertilized eggs. When this suitable spawning ground is found, the yellow croaker will gather here and wait for the opportunity. During the spawning process, the fish's body is always twisting. Because of the extrusion and collision of the male fish, the female fish's body is often lifted out of the water, and the flapping of the fish's tail will also form obvious splash on the water, which will decorate the spawning ground with vitality. When the water temperature is between 7℃ and 17℃, they will begin to perform spectacular underwater ballet.
Female fish do not lay eggs all at once. It migrates a long way, spawns a batch when it matures, and then continues to migrate. It takes more than a month to spawn two or three times along the way, and the longest migration distance can reach more than 60 kilometers. A female fish can lay more than 3,000 eggs a year, but it can grow up smoothly. After 3 to 5 years, only 3 to 5 adult fish will return to this river to lay eggs.
How hard it is to go upstream
The yellow croaker has just passed a cold and hunger winter in Qinghai Lake, and it is already very weak. Moreover, during the whole process of going upstream, they are hungry and don't eat, and they are even less energetic. The velocity of water has become the first difficulty in their progress. If the water flows too fast, it will wash them down, so their forward route is to advance and retreat at the same time. It is possible to advance 5 kilometers and be pushed back 3 kilometers by the water. If we catch up with the heavy rain and the rising water in the upper reaches of the river, we can clear up all their efforts for several days in one night. Yellow croaker heads upstream against the water, and the farthest destination is 60 kilometers away. It takes them more than a month to swim, and on average, they can't swim two kilometers a day, which shows how hard it is to swim upstream.
In addition to the flow rate of water, the yellow croaker will accidentally encounter the second level, which is the drop of the river. It is impossible for all the rivers to have the same slope, so that the yellow croaker can go upstream slowly. Maybe there will be such a gap somewhere. The body length of most yellow croaker is only 20 to 30 centimeters, and the jumping height is about one meter. The height of this drop, coupled with such a rapid current, may be an insurmountable hurdle for many fish. But the yellow croaker must jump up, and they will never give up. As a result, many fish will be confused and seriously injured.
The sad gate of death on the way to migration